Environmental Stress-Sensing and Pathogenicity in Cryptococcus neoformans

Cellular stress can be defined as the damage caused to macromolecular systems when the cell is exposed to acute environmental changes, while a stress response is a conserved mechanism of resistance to these damages (Kultz 2003). Cryptococcus neoformans, like most pathogens, not only has to cope with substantial changes in its natural environment, but must also respond and proliferate in a variety of conditions found within the host. As with most pathogenic microbes therefore, appropriate responses to stress are key elements for survival in the host. The stresses C. neoformans encounters within its host include oxidative stress, nitrosative stress, osmotic shock, high temperature, hypoxia, nutrient deprivation, changes in pH, low- calcium and iron deprivation (Brown et al. 2007). Several signaling pathways mediated by the Hog1p, protein kinase C (pkC) and calcineurin/calmodulin allow this fungus to sense and respond to stress. However, the mechanisms underlying stress responses in C. neoformans are not completely understood. Recent genomic and proteomic approaches have allowed us to gain further understanding of the stress responses in C. neoformans. In this chapter, the current knowledge on individual genes, pathways and transcription factors which are essential for stress resistance in C. neoformans are discussed.